The Anomalous Case of Axion EFTs and Massive Chiral Gauge Fields

TL;DR

This paper explores how axion EFTs interact with massive chiral gauge fields, revealing that anomaly-based sum rules are violated when chiral matter is integrated out, with implications for Standard Model extensions.

Contribution

It demonstrates that axion couplings to massive chiral gauge fields do not solely originate from anomalous EFT terms and examines the implications for anomaly matching in the Standard Model.

Findings

Anomaly sum rules are violated in the presence of chiral matter.

Axion interactions with massive gauge fields involve non-anomalous contributions.

A chiral extension of the Standard Model can be consistent with experimental constraints.

Abstract

We study axion effective field theories (EFTs), with a focus on axion couplings to massive chiral gauge fields. We investigate the EFT interactions that participate in processes with an axion and two gauge bosons, and we show that, when massive chiral gauge fields are present, such interactions do not entirely originate from the usual anomalous EFT terms. We illustrate this both at the EFT level and by matching to UV-complete theories. In order to assess the consistency of the Peccei--Quinn (PQ) anomaly matching, it is useful to introduce an auxiliary, non-dynamical gauge field associated to the PQ symmetry. When applied to the case of the Standard Model (SM) electroweak sector, our results imply that anomaly-based sum rules between EFT interactions are violated when chiral matter is integrated out, which constitutes a smoking gun of the latter. As an illustration, we study a UV-complete chiral extension of the SM, containing an axion arising from an extended Higgs sector and heavy fermionic matter that obtains most of its mass by coupling to the Higgs doublets. We assess the viability of such a SM extension through electroweak precision tests, bounds on Higgs rates and direct searches for heavy charged matter. At energies below the mass of the new chiral fermions, the model matches onto an EFT where the electroweak gauge symmetry is non-linearly realised.